The present invention relates to a method of making vehicle body panels by blow molding.
Conventional vehicle body panels are formed by an outer steel panel and an inner steel panel that are welded together. For example, an inner roof panel may include integrally formed reinforcing sections or reinforcements may be welded to the inner roof panel to provide added strength in particular locations. Steel roofs are strong but relatively heavy and manufacturing processes involved are labor-intensive.
Recently, injection molded vehicle body panels have been developed. For example, an outer roof panel and an inner roof panel may be separately injection molded and then bonded together in a secondary operation. Fasteners may also be used to supplement bonding the inner and outer roof panels together. This process is slow and labor-intensive, requiring many steps to form the roof and then assemble the roof panels together. In particular, the inner roof panel must be designed with reinforcing ribs and gusset walls to provide strength. One problem associated with injection molding an outer roof panel is that surface imperfections caused by shrink marks are created in the injection molding die. An inherent problem for large, relatively thin injection molded panels that are used for vehicle applications is the tendency of the panels to distort or vibrate when air flow and air pressure differentials are applied to the moving vehicle.
Rotational casting is a plastic processing technique that has been proposed for high strength applications. However, rotational casting of plastics results in a relatively heavy finished product that is expensive and may not always meet close tolerance requirements.
Blow molding is a efficient and economical plastic processing technique that is most commonly associated with forming PET beverage containers. One problem associated with blow molding is that it is difficult to maintain close tolerances. While it is possible to form sharp edges and corners by blow molding, it is difficult to consistently form these design elements. Another problem with blow molding techniques is the difficulty in maintaining consistent wall thickness in larger parts.
These problems encountered by prior art vehicle body panel designs and available plastic processing techniques are addressed by the present invention as summarized below.
It is a principal object of the invention to make a body panel that has a blow molded portion that makes up the majority of the body panel. Injection molded end caps and edge interfaces are secured at predetermined locations where close tolerances must be held. This approach provides an economical, strong body panel that is lower in cost and lighter in weight than multi-panel steel or injection molded body panels.
The present invention relates to providing a body panel for a vehicle that comprises a blow molded body panel having single wall portions and double wall portions. Attachments are secured to the edges of the blow molded panel wherein the attachment pieces have close tolerance elements or seals that are fit to other parts of the vehicle.
In one embodiment of the invention, a roof panel comprising a substantially horizontal roof section that is blow molded with a plurality of pillar extensions that extend generally downwardly from the horizontal roof section. The pillar extensions are initially formed by blow molding and have closed ends that are subsequently cut off to provide open ends. A plurality of separately formed end inserts are assembled to the open ends. The end inserts may be injection molded or metal parts.
According to another aspect of the invention, the roof panel comprises a substantially horizontal roof section that is completely blow molded with at least one closed edge that is cut off, leaving an edge opening. At least one separately formed edge insert is assembled to the edge opening.
According to the method of making a body panel for a vehicle of the present invention, a blow molding parison is formed and loaded into a blow molding die. Air is injected into the parison to expand the parison, filling the die and forming a blow molded body having integrally formed reinforcements. The blow molded body is cooled in the die and then removed. The end portions of the blow molded body are then partially cut off to form receptacles in which interface parts are inserted.
According to another aspect of the invention, as applied to making a roof assembly, the end portions of the blow molded body are adapted by the interface parts to mount to A, B and C pillars of the vehicle. The blow molded body has double wall portions and single wall portions that are arranged to provide localized areas of increased structural strength. The double wall portions may be located to provide wiring ducts or accessory mounting locations.
According to yet another aspect of the invention, the method may include the step of assembling a seal retainer on the blow molded body in a location where a seal is to be attached to the body panel. Alternatively, the method may include the step of assembling a window or door frame element to an edge of the blow molded body.
The method of the present invention may comprise forming a vehicle body panel by an injection molding process and then subsequently assembling trim pieces to the blow molded body formed in the blow molding process. One or more side edge portions of the blow molded body may be cut off to form a blow molded body having one or more openings into which a separately formed side edge insert may be assembled. Two side edge portions may be formed and adapted to receive two side edge portions. The side edge portions can be either the right and left sides or the front and rear edges of the blow molded body making up the body panel. Alternatively, four side edge portions can be cut off from the blow molded body to allow for the insertion of four side edge inserts on all four sides of the body panel assembly.
According to a further aspect of the invention, the trim pieces applied to the blow molded body may be seals that are secured to the periphery of the blow molded body. The seals may form an interface with adjacent components. The adjacent components may be frame members of the vehicle or side and rear panels forming a part of the passenger compartment and storage compartment enclosure.